1. Field of the Invention
The present invention relates to a method for generating a double-speed instantaneous decoding refresh (IDR)-unit for trick play, and a trick play system and method using the same. More particularly, a double-speed IDR-unit for trick play is generated by controlling the number and data size of video frames in a trick play system, so that a bit rate of original contents can be maintained and a load on a server can be minimized, thereby controlling a trick play speed.
The IDR-unit includes an IDR frame and all prediction frames between an IDR frame and the next IDR frame. The double-speed IDR-unit represents a group of frames to be “transmitted” at a time during a trick play, and the double-speed IDR-unit includes the IDR frame and prediction frames which are selected based on predetermined conditions.
This work was supported by the Information Technology (IT) research and development program of the Korean Ministry of Information and Communication (MIC) and the Korean Institute for Information Technology Advancement (IITA) [2005-S-405-02, “A Development of the Next Generation Internet Server Technology”].
2. Description of Related Art
In a video on demand (VoD) system, the support of a trick play function similar to a fast forward function of a video cassette recorder (VCR) is very important in view of a user's convenience.
Many methods for implementing the trick play of the VoD system have been developed. Examples of the methods include a frame periodic selection method, a group of picture (GOP) level selection method, and a trick-play dedicated content generating method, based on Moving Picture Experts Group-4 (MPEG-4) or H.263 contents.
There are two types of trick play methods.
The first method is to implement a trick play speed by periodically removing frames from original contents. This method can efficiently control the trick play speed without placing a load on a server, but it cannot maintain a bit rate because the trick play speed is implemented by regularly selecting frames without considering a size of a compressed frame.
If the bit rate is changed, an incorrect bit rate is informed to the terminal in an initial setting operation through a control protocol such as Real-Time Streaming Protocol (RTSP) when a streaming begins. Since hardware of the terminal may cause a malfunction of a buffer, a correct streaming is difficult.
The second method is to transmit trick-play contents encoded from the original contents. It is a simple encoding method for allowing a server to control a bit rate of contents in real time. This method can solve the problem of the first method, but it may degrade a real-time characteristic. Further, only if the encoding, either simple or complicated, is performed, a heavy load is placed on a server when a plurality of terminals are connected. Since the algorithm of H.264 standard is more complex than that of an existing video compression standard, the load on the server increases.
Therefore, there is a need for methods that can provide a high-speed effect in an H.264 system by correctly transmitting the contents while maintaining the bit rate of the original contents.